The present invention relates generally to systems and apparatus for processing whole blood, and more specifically to a pressure cuff draw mode enhancement system and method for a single needle in vivo blood fractionation apparatus.
Various methods and apparatus have been developed for the in vivo processing of whole blood, wherein the whole blood is taken from a donor, a desired blood component is separated and collected, and the processed blood is returned to the donor. Blood components typically collected using such processing include plasma (plasmapheresis), white blood cells (leukopheresis) and platelets (plateletpheresis).
In vivo blood processing apparatus may be of the centrifugal type, wherein the differing density of the collected blood component causes the component to congregate for collection at a particular radial distance in a centrifuge, or may be of the filter type, wherein the particle size of the collected component allows only that component to pass through a filter membrane into a collection chamber. Filter type apparatus is generally preferable for in vivo plasmapheresis applications, since such apparatus does not require complex rotating machinery and is more compact and less costly to manufacture.
One form of filter which is particularly attractive for use in plasmapheresis apparatus utilizes a plurality of parallel microporous hollow fibers arranged side-by-side in the form of a bundle within a hollow cylinder. As whole blood is caused to flow through the fibers the plasma component passes through the walls of the fibers to the surrounding container, which forms a collection chamber from which the component is transported to a collection container. A preferred construction and method of manufacture of such a flow-through hollow fiber filter is shown in the copending application of Robert Lee and William J. Schnell entitled, "Microporous Hollow Fiber Membrane Assembly and Its Method of Manufacture", Ser. No. 278,913, filed June 29, 1981, now abandoned.
The efficiency of a flow-through filter in separating plasma from whole blood depends on the hematocrit of the donor, and the flow rate and pressure of the whole blood as it is pumped through the filter. Insufficient flow rates or whole blood pressure results in less than optimum yields. Excessive flow rates or whole blood pressures results in hemolysis, or damage to the red blood cells within the filter, and possible failure of the filter to exclude red cells from the collected plasma. Thus, a practical limit exists for the percentage of plasma that can be recovered by a flow-through membrane filter in a single pass of whole blood.
To improve the efficiency of blood fractionation systems it has been proposed that once-filtered whole blood be recirculated through the filter. This enables the filter to refilter previously-filtered whole blood, recovering an additional percentage of the remaining plasma component. A blood fractionation system providing such recirculation is shown in the copending application of Arnold C. Bilstad et al, entitled "Increased Yield Blood Component Collection System and Methods", Ser. No. 411,057, filed Aug. 24, 1982.
However, in certain procedures, as where a high hematocrit is encountered in whole blood drawn from a donor, the hematocrit of the once-filtered whole blood may be so high as to require a reduction in the filter rate and pressure with an attendant reduction in filter efficiency, to avoid hemolysis in the second pass. Furthermore, for user comfort it is desirable that in vivo blood fractionation systems withdraw whole blood from and return whole blood to the donor through a single phlebotomy needle at a single injection site. This necessitates either the use of a single dual-lumen phlebotomy needle, in conjunction with a continuous flow non-batch system, such as described in the copending application of Arnold C. Bilstad et al, entitled "Blood Fractionation Apparatus", Ser. No. 330,989, filed Dec. 15, 1981, or of a single-lumen phlebotomy needle in conjunction with a bidirectional batch system, whereby batches of whole blood are alternately drawn through the needle, passed through a plasma separation filter, and returned through the same needle. Such bidirectional single-lumen batch systems have the advantage of utilizing a smaller and potentially less traumatic single lumen needle.
A preferred single lumen batch-type blood fractionation system which provides operator-controlled partial recirculation during return cycles to reduce processing time and accommodate variations in the hematrocrit of the processed whole blood is described in the copending application of Arnold C. Bilstad et al, entitled "Single Needle Blood Fractionation System Having Adjustable Recirculation Through Filter."
Basically, this system provides for user-controllable recirculation of whole blood through the system filter, thereby maintaining filter operating efficiency notwithstanding variations in whole blood hematocrit. Whole blood is drawn from the donor through a phlebotomy needle and associated bidirectional donor conduit and pumped through the system filter to a reservoir by an inlet pump. Upon the volume of fluid in the reservoir reaching a predetermined level, plasma-deficient whole blood is pumped from the reservoir to the donor conduit by a return pump, which operates at a higher rate than the inlet pump. By reason of the higher rate of the return pump flow is reversed in the donor conduit and processed whole blood is returned to the donor through the phlebotomy needle, without the need for valves for controlling fluid flow in the system. By controlling the relative speeds of the inlet and return pumps during the draw and return cycles, the percentage of recirculation can be varied to maintain a desired hematocrit at the filter.
To minimize inconvenience to the donor it is desirable that whole blood be withdrawn, processed and returned at as high a rate as possible. The use of a pressure cuff for improving the draw rate in a batch-type system, installed at a location above the system phlebotomy needle, and actuated during draw cycles and terminated in response to the weight of collected plasma corresponding to a completed batch, is shown in U.S. Pat. No. 4,086,924. However, no provision is made in this reference for controlling the pressure cuff in response to the volume of processed fluid in an intermediate reservoir.
A blood fractionation system incorporating a pressure cuff and control system responsive to the weight of an intermediate fluid reservoir is shown in the copending application of Arnold C. Bilstad et al, "Single Needle Blood Fractionation System Having Pressure Cuff Draw Mode Enhancement". The present invention is directed to a pressure cuff draw mode enhancement system and method operable with this fractionation system, wherein a pressure cuff is automatically pressurized upon the volume of filtered whole blood in an intermediate reservoir reaching a predetermined maximum level, and depressurized upon the volume in the reservoir falling below a predetermined minimum level, in conjunction with the operation of a return pump connected to return and/or recirculate the filtered whole blood.
Accordingly, it is a general object of the present invention to provide a new and improved pressure cuff draw mode enhancement system.